1. Field of the Invention
The present invention relates to a polyester production method, a polyester composition, and a polyester fiber.
2. Description of the Related Art
Polyester is employed in a wide variety of uses due to the usefulness of the functions thereof, such as in clothing, material, medical, and other applications.
Generally, in the production of polyester, antimony compounds are widely used as a polymerization catalyst in industrial processes for manufacturing high-molecular-weight polymers. However, polymers containing antimony compounds have several undesirable properties, as follows.
For example, at the time of melt-spinning of polyester obtained with antimony compounds as a polymerization catalyst, there is residual antimony compound which accumulates around the spinneret. This accumulation of the residual antimony compound is thought to be due to the antimony compound being denaturized near the spinneret, of which a part vaporizes and dissipates, leaving a component which is primarily antimony at the spinneret. Progression of this accumulation leads to defective filament, and accordingly must be periodically removed.
Also, residual antimony compounds readily form relatively large pieces of foreign matter. This is undesirable since it can cause increased pressure at the filter in the forming process, thread breakage during spinning, film damage in formation of films, and so forth, and has been a factor in reduced operation capabilities. Due to such reasons, there is the need for a polyester containing little or no antimony.
An known example thereof is employing a germanium compound instead of an antimony compound as the polymerization catalyst, but there is little germanium deposited which can be mined and germanium is rare, so general-purpose application thereof is not practical.
Also, a technique for using titanium complexes formed of titanium compounds and phosphorous compounds as a polymerization catalyst are disclosed in PCT Japanese Translation Patent Publication No. 2001-524536, PCT Japanese Translation Patent Publication No. 2002-512267, Japanese Unexamined Patent Application Publication No. 2002-293909, Japanese Unexamined Patent Application Publication No. 2003-40991, and Japanese Unexamined Patent Application Publication No. 2003-40994. While this method allows the amount of pieces of foreign matter to be reduced, the color tone of the obtained polymer is not quite suitable for actual use.
Further, Japanese Unexamined Patent Application Publication No. 2003-147060 discloses a technique for producing a copolymerized polyester having phenylene dioxydiacetic acids as a copolymerization component, wherein polycondensation is carried out under the presence of a polymerization catalyst and an organic phosphite compound. However, this Publication makes no mention of the specific chemical structure of the titanium compound. Also, the only polymerization catalyst described in the Embodiments of this Publication is an antimony compound, and accordingly does not lead to solving the cause of increased pressure at the filter in the forming process, thread breakage during spinning, and film damage in formation of films.